When I was in school a favorite class of mine outside of design was photography. At the time digital photography was in its infancy and was extremely expensive for even businesses to pursue, so I learned how to work with film. Many of the tools you use today in Photoshop originated in darkrooms like the one I spent many hours in myself. The article linked below specifically discusses the origins of dodging and burning and how you can use them today to enhance your digital photos. Enjoy!